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SCL

SDA

SCL_SINK

SDA_SINK

OVS

SCL_SINK/

SDA_SINK

SCL/SDA

Vcc

0.5V

5V +

10%

Vcc/2

PLH

I2C Enable

5V_PWR

I2CEN

5V_EN

TMDS442

SLLS757A – AUGUST 2006 – REVISED MARCH 2007

or not connected, VOL is typically 0.5 V. When OVS is connected to GND, VOL is typically 0.65 V. When OVS is

connected to VCC, VOL is typically 0.8 V. VOL is always higher than the driver R input threshold, VIL, which is

typically 0.4 V, preventing lockup of the repeater loop. The VOL value can be selected to improve or optimize

noise margins between VOL and the VIL of the repeater itself or the VIL of some external device connected on the

T side.

When the R side is pulled up, above 1.5 V, the T side driver turns off and the T side pin is high impedance.

Figure 33. I2C Drivers in TMDS442

When the T side is pulled below 0.4 V by an external I2C driver, both drivers R and T are turned on. Driver R

pulls the R side to near 0 V, and driver T is on, but is overridden by the external I2C driver. If driver T is already

on, due to a low on the R side, driver R just turns on.

When the T side is released by the external I2C driver, driver T is still on, so the T side is only able to rise to the

VOL of driver T. Driver R turns off, since VOL is above its 0.4-V VIL threshold, releasing the R side. If no external

I2C driver is keeping the R side low, the R side rises, and driver T turns off once the R side rises above 1.5 V,

see Figure 34.

Figure 34. Waveform of Turning Driver T Off

It is important that any external I2C driver on the T side is able to pull the bus below 0.4 V to ensure full

operation. If the T side cannot be pulled below 0.4 V, driver R may not recognize and transmit the low value to

the R side.

The I2C drivers are enabled with an internal EN signal. This EN signal is the AND gate result of the 5V_PWR

signal from the selected input port and the I2CEN signal for the output. This AND gate is turned on based on an

OR gate result of the GE and the 5V_EN settings.

Figure 35. I2C Enable Equivalent Logic

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